Refactor agent form UX: add section rail layout and Memory placeholder

[esafwan]

Motivation

• Provide a reusable, future-proof base for the Agent form UI so tabs can be composed from smaller sections and the form surface scales without becoming a god-component.
• Surface the forthcoming Memory tab in the UI as a disabled/coming-soon preview while preventing use until backend integration is merged.
• Preserve existing behavior, validation and provider/model wiring while making layout and section metadata reusable across tabs.

Description

• Added a small form-base component set: SectionRailLayout and SectionBlock to render a left-side section rail with status dots and anchor navigation (frontend/src/components/agent/form-base/SectionRailLayout.tsx).
• Refactored GeneralTab to the new section-rail layout and split it into Identity, Model, and Instructions sections while keeping provider/model filtering, sliders and the instructions textarea (frontend/src/components/agent/GeneralTab.tsx).
• Refactored BehaviorTab to the section-rail pattern and split it into Chat Access, History, and Execution sections while keeping the existing cross-field logic and toasts (frontend/src/components/agent/BehaviorTab.tsx).
• Added a non-interactive Memory tab placeholder marked “Coming Soon” so the structure is visible but inputs are disabled until the feature is merged (frontend/src/components/agent/MemoryTab.tsx) and wired the tab into AgentFormPage (updated tab config and tab bar columns) (frontend/src/pages/AgentFormPage.tsx).

Testing

• Ran ESLint for the new/updated files with npx eslint src/components/agent/GeneralTab.tsx src/components/agent/BehaviorTab.tsx src/components/agent/MemoryTab.tsx src/components/agent/form-base/SectionRailLayout.tsx and the checked files passed without errors.
• Ran type checking with npm run typecheck and it failed due to a pre-existing, unrelated TypeScript type mismatch in src/components/agent/TriggerModal.tsx; the type error is not introduced by these changes and requires a separate fix.

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Codex Task